Impressed current anodes are made from a variety of materials such as graphite, titanium, or high silicon cast iron. High silicon cast iron is a particularly effective material and is widely used in impressed current cathodic protection systems. The cast iron anodes may be of substantial length and are usually in tubular or solid form. Elongated anodes suffer from a phenomena known as "pencil effect" or "end effect". The anodes are, of course, designed to corrode rather than the structure being protected. With the pencil effect the anode corrosion occurs at each end in effect sharpening each end progressively as a pencil. The pencilling continues throughout the service life of the anode usually until the progressive corrosion meets the electrical connection to the anode. When the electrical connection fails, the anode is no longer effective.
Solid anodes can be more effective and have a longer service life primarily because of the greater mass of cast iron material involved. Tubular high silicon cast iron anodes can be rotationally cast much like a section of cast iron pipe. Solid anodes usually require sand or special molds and patterns. Another problem with solid high silicon cast iron anodes is that unlike graphite or other metals they are quite brittle and cannot be economically drilled to any significant extent. For this reason electrical connections for solid elongated sizable high silicon cast iron anodes are usually cast into the anode near one end, and the pencilling or end effect reduces the service life of the anode. An example of such a connection is seen in Sumner U.S. Pat. No. 3,471,395. Such patent also discloses a complex heat shrinkable fluorocarbon sheath surrounding the connection end and a plastic end cap, all designed to provide added protection to the connection. It would, of course, be desirable in an anode of the type shown in Sumner to have the connection at approximately the midpoint of the anode end-to-end.
Providing a midpoint or center connection is relatively easy in tubular cast iron anodes such as seen in Bushman U.S. Pat. No. 4,515,669 or in tubular titanium anodes such as seen in Pfaller et al. U.S. Pat. No. 5,185,921. However, where the connection is to be positioned at the bottom or blind end of a fairly deep hole, complex apparatus is usually required. An example is seen in Tatum U.S. Pat. No. 4,265,725 where a hydraulic cylinder assembly and frame are required with the frame being longer than the anode, the cylinder, and the stroke of the cylinder. For an anode of substantial length an overhead crane may be required to assemble the parts.
It would accordingly be desirable to have a solid elongated cast iron anode with a reliable midpoint connection, and one with a connection which can easily be made to be seated in the bottom or blind end of a small hole extending from one end.